This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Several studies have used arterial spin labeling (ASL) approaches to investigate the regional CBF changes with hyperoxia. Although it is well-known that inhaled oxygen creates a significant reduction in the T1 of arterial blood (T1a), and that T1a has a substantial effect on CBF measurements using ASL, only a small number of these studies have incorporated these T1a changes in their CBF calculations. For these studies, some investigators used the results of prior studies of T1a during hyperoxia to estimate an average expected change in T1a. Others were required to model the expected change in T1a because the study was performed at 3 Tesla (T), where there is no literature data available on T1a during hyperoxia. These approaches may be problematic for several reasons. In this project, our aim was to simultaneously measure CBF and T1a in vivo during normoxia and hyperoxia using pulsed ASL approaches. This will allow for an accurate correction of CBF data due to reduction in T1a on a per subject basis, allowing for the quantification of the degree to which the reduction in CBF measured with ASL are due to T1a. Rats are used as animal model in this case because of the complication of spins flowing in from outside of the transmit coil.